Pigs may be organ sources in as few as 5 years

Animals' genes being altered so they can be used by humans

Daniel Q. Haney, The Associated Press

Published
10:00 pm PST, Sunday, February 17, 2002

BOSTON -- Transplanting genetically modified hearts and other organs from pigs to people could be possible in five to seven years, but many scientific and ethical questions remain, scientists said yesterday.

Researchers are changing pigs' genes to "humanize" their organs, making them more like people's so they will serve as alternatives to human cadavers for transplanted organs.

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Yesterday's meeting came after an important milestone last month. Two companies said they have produced litters of cloned miniature pigs that lack one copy of a gene that makes pig parts incompatible with human immune defenses.

In January, Immerge BioTherapeutics and PPL Therapeutics both said they had created pigs that lack one of the two usual copies of a gene that makes a sugar called alpha-1-galactose.

This sugar lines pig blood vessels. Because it is nearly identical to a bacterial sugar, the human immune system attacks it.

As a result, pig organs transplanted into people are destroyed almost instantly.

Immerge's pigs were born in September and October and PPL's in December. The next step will be to breed these pigs with each other. Cooper said efforts to do this should begin within two months as the oldest animals reach sexual maturity.

There is a 1-in-4 chance that each offspring will be born with no copies of the gene. No one knows for sure whether pigs can survive without alpha-1-galactose. But if they can, the animals could be raised to supply hearts and kidneys for human transplants.

Scientists will have to test the process first by transplanting the pig organs into other animals, such as baboons. Another worry is whether the organs will carry pig viruses that could be harmful to people, especially if they spread from the organ recipient to others.

Bach said people should debate whether the risk, however remote, is worth taking.

"We live in a world of risk, and this is an additional risk," said Bach. "If the medical establishment imposes this on the public and there is a potential risk, I feel ethically we have to go to the public."

However, Cooper said the decision should be left to regulatory agencies, which have the expertise to wade through the highly technical arguments on both sides.

All pig cells carry a so-called retrovirus that is harmless to them, but no one knows what it might do to humans. Scientists are working with a strain of pigs that cannot spread this virus to human cells. However, Bach said he is concerned about possible pig viruses that have not been discovered yet.

Cooper responded that scientists can only guard against viruses and other hazards that have been identified. "You deal with all the known problems, but if you worry about unknown problems you will never make any success in any branch of science," he said.

According to the United Network for Organ Sharing, about 77,000 Americans are in line for transplants each year, while 23,000 actually receive them. Demand is growing five times faster than the supply, and many who could benefit never even make the waiting list, because they have other health problems.

In other health news yesterday:

A government official said in the event of a bioterror attack using smallpox, health authorities could stretch out the nation's limited vaccine supply simply by diluting the 15 million doses that are on hand. Experiments to see whether diluted smallpox vaccine could still offer protection against the disease have been "very successful," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. Fauci spoke in Boston at the same meeting as the pig transplants were discussed.

His team's most recent study, published online Saturday in the journal Neuron, is the first to give clear evidence that aging does not physically destroy the cognitive mechanisms responsible for effective memory creation in the frontal lobes of the brain. Rather, aging simply makes it increasingly difficult for older adults to spontaneously access those regions.